1、4/5×1/2＋2/5÷0.6－1/15

4/5×1/2+2/5÷0.6-1/15
=2/5+10/15-1/15
=6/15+10/15-1/15=1
1/1×3＋1／3×5＋1／5×7＋.＋1/17×19＋1/19×21
=1/2×(1-1/3+1/3-1/5+1/5-1/7.+1/19-1/21）
=1/2×（1-1/20）
=10/21
9999*2222+3333*3334
=3333×3×2222+3333×3334
=3333×6666+3333×3334
=3333×(6666+3334)
=3333×10000
=33330000
【（8 又5/8-4.625）÷（2.4＋1又3/5）】×50％
=【（8又5/8-4又5/8）÷（2.4+1.6）】×0.5
=【4÷4】×0.5
=0.5

1，
1
2，
1/1*3=1/2(1-1/3)
1/3*5=1/2(1/3-1/5)
1/19*21=1/2(1/19-1/21)
原式=1/2（1-1/3+1/3-1/5+。。。-1/19+1/19-1/21）=1/2（1-1/21）=
10/21
3，
9999*2222+3333*3334
=3333×3×22...

1、
=2/5+2/5÷3/5-1/15
=2/5+2/5×5/3-1/15
=2/5+2/3-1/15
=6/15+10/15-1/15
=15/15
=1
2、